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The present invention relates to ladders and more particularly devices for leveling ladders on uneven surfaces and more specifically devices for automatically leveling ladders.
Setting a ladder firmly on uneven ground is commonly achieved by using wood blocks and shims. Many patents have been granted for devices which attach to the ladder and provide some adjustment to accommodate the uneven ground. Commercial success of these devices has been limited, all of them being handicapped by some inconvenience in attachment to the ladder or in operation.
For example, U.S. Pat. No. 5,273,133 by Thocher, et.al. while purporting to provide automatic adjustment, does not provide infinite resolution in the compensation for height variation, is not easily attached and removed from the ladder, does not improve the lateral stability of the ladder and is not a simple design which would permit relatively inexpensive manufacture. Infinite resolution of the set up is achieved by the screw jack of U.S. Pat. No. 4,744,441 by Sandstrom but it is not automatic, requiring the operator to turn the screw in or out to accommodate terrain differences. U.S. Pat. No. 5,609,222 by Horbacewicz discloses a device which may attach easily to a ladder, however the set up is not automatic and resolution is course because the extension of the leg attachment is determined by a pin in one of a row of holes. Additionally, prior art ladder levelers generally do not provide for an increase in the stability of the ladder beyond that of the bare ladder. Thus, there remains a need in the art for a ladder leveler which addresses the deficiencies of the prior art devices.
It is therefore an objective of the present invention to provide a ladder leveler that will automatically set up and lock to compensate for terrain height variations at each leg.
It is a further objective of the invention to provide relatively fine resolution in the compensation for height variation,.
A further objective of the invention is to provide a device which may be easily attached or removed from the ladder.
Another objective is to improve the lateral stability of the ladder by providing a wider stance for the ladder.
These and other objectives are met by the present invention, which includes a base member adapted to be secured to the ladder and first and second arms pivotably mounted on the base member. The arms have lock ends and opposite support ends. A locking member is also pivotably mounted on the base member between the arms such that the lock end of each arm bears against the locking member. The arms and locking member are arranged such that a force applied to one arm as a result of resting the device on the ground causes the locking member to bear against the opposite arm thereby conforming the arms to the uneven ground profile and supporting the ladder. In one embodiment, the locking member has concave bearing surfaces against which the lock ends of the arms bear.
Preferably, the locking member is shaped such that an angle between a tangent at the contact point between the lock end of an arm and the locking member and a tangent to an arc described by the motion of the arm lock end is between about 12 and 20 degrees.